The guy hanging upside down is... right behind her. She sees him standing and thinks: ok, so that proves that I'm just hallucinating, better ignore it. But then the guy points at his gutted self and screams. So he sees it too, so it's real! But maybe she's hallucinating him and the dead one is the real thing! But maybe she's hallucinating both! She has enough of it, screams and punches him (the standing one) in his stupid face. It turns out it was Milo. She's not strong enough to kill Milo with her bare fists, but he was holding his mug of hot coffee and spills it all over himself and dies from the burns.

More serious theory: this guy was captive with her in the Wastes, and the captors had fun torturing him to death. She was present when they did and could have at least tried to untie him while they were out getting more beer, but she was too scared to come out of hiding and left him be, and when they came back it was partly her fault he died.

So Jenny is just setting up the idea that each of the characters is deeply flawed or evil and deserve to die? That the zombies are at least true to their nature and don't pretend to be something the aren't?